1. Field of the Invention
This invention relates generally to a motor vehicle driveline, which in operation transmits power continually to a first wheel set and selectively to a second wheel set.
2. Description of the Prior Art
Power transfer unit (PTU) efficiency is a concern in all wheel drive (AWD) vehicles derived from front wheel drive vehicle platforms, partially due to kinematics dictated by the speed and torque of the transmission output. For example, an AWD powertrain typically reduces fuel economy by about five percent compared to a front wheel drive (FWD) powertrain.
Driveline disconnects are a well established fuel economy improvement method in rear wheel drive powertains, but are absent from FWD products. A principal difference between FWD-based and RWD-based AWD products is the transfer case used on RWD-based products provides a convenient disconnect point. In FWD-based powertrains, the relatively small package space available for the power transfer unit makes implementation of driveline disconnects on FWD-based products very challenging.
A need exists in the automotive industry for a front disconnect located ahead of a power takeoff unit in order to optimize fuel efficiency of the powertrain by minimizing in FWD operation the number of rotating components when AWD is not selected. Preferably the package space required for the disconnect permits the PTU drive system to be located within the transaxle case.